3,412 research outputs found
Precession-torque-driven domain-wall motion in out-of-plane materials
Domain-wall (DW) motion in magnetic nanostrips is intensively studied, in
particular because of the possible applications in data storage. In this work,
we will investigate a novel method of DW motion using magnetic field pulses,
with the precession torque as the driving mechanism. We use a one dimensional
(1D) model to show that it is possible to drive DWs in out-of-plane materials
using the precession torque, and we identify the key parameters that influence
this motion. Because the DW moves back to its initial position at the end of
the field pulse, thereby severely complicating direct detection of the DW
motion, depinning experiments are used to indirectly observe the effect of the
precession torque. The 1D model is extended to include an energy landscape in
order to predict the influence of the precession torque in the depinning
experiments. Although preliminary experiments did not yet show an effect of the
precession torque, our calculations indicate that depinning experiments can be
used to demonstrate this novel method of DW motion in out-of-plane materials,
which even allows for coherent motion of multiple domains when the
Dzyaloshinskii-Moriya interaction is taken into account
The Quest for the Heaviest Uranium Isotope
We study Uranium isotopes and surrounding elements at very large neutron
number excess. Relativistic mean field and Skyrme-type approaches with
different parametrizations are used in the study. Most models show clear
indications for isotopes that are stable with respect to neutron emission far
beyond N=184 up to the range of around N=258.Comment: 4 pages, 5. figure
The Sloan Lens ACS Survey. VI: Discovery and analysis of a double Einstein ring
We report the discovery of two concentric Einstein rings around the
gravitational lens SDSSJ0946+1006, as part of the Sloan Lens ACS Survey. The
main lens is at redshift zl=0.222, while the inner ring (1) is at zs1=0.609 and
Einstein radius . The wider image separation () of the outer ring (2) implies that it is at higher redshift. Its
detection in the F814W filter implies zs2<6.9. The configuration can be well
described by a total density profile with
and velocity dispersion \sigma_{SIE}=287\pm5\kms. [...] We consider whether
this configuration can be used to constrain cosmological parameters exploiting
angular distance ratios entering the lens equations. Constraints for
SDSSJ0946+1006, are uninteresting due to the sub-optimal lens and source
redshifts. We then consider the perturbing effect of the mass associated with
Ring 1 building a double lens plane compound lens model. This introduces minor
changes to the mass of the main lens and allows to estimate the mass of Ring 1
(\sigma_{SIE,s1}=94\pm30\kms). We examine the prospects of doing cosmography
with a sample of 50 double lenses, expected from future space based surveys
such as DUNE or JDEM. Taking full account of the model uncertainties, such a
sample could be used to measure and with 10% accuracy, for a
flat cosmology
The initial mass function of early-type galaxies
We determine an absolute calibration of the initial mass function (IMF) of
early-type galaxies, by studying a sample of 56 gravitational lenses identified
by the SLACS Survey. Under the assumption of standard Navarro, Frenk & White
dark matter halos, a combination of lensing, dynamical, and stellar population
synthesis models is used to disentangle the stellar and dark matter
contribution for each lens. We define an "IMF mismatch" parameter
\alpha=M*(L+D)/M*(SPS) as the ratio of stellar mass inferred by a joint lensing
and dynamical models (M*(L+D)) to the current stellar mass inferred from
stellar populations synthesis models (M*(SPS)). We find that a Salpeter IMF
provides stellar masses in agreement with those inferred by lensing and
dynamical models (=0.00+-0.03+-0.02), while a Chabrier IMF
underestimates them (=0.25+-0.03+-0.02). A tentative trend is
found, in the sense that \alpha appears to increase with galaxy velocity
dispersion. Taken at face value, this result would imply a non universal IMF,
perhaps dependent on metallicity, age, or abundance ratios of the stellar
populations. Alternatively, the observed trend may imply non-universal dark
matter halos with inner density slope increasing with velocity dispersion.
While the degeneracy between the two interpretations cannot be broken without
additional information, the data imply that massive early-type galaxies cannot
have both a universal IMF and universal dark matter halos.Comment: 10 pages 4 figures. Resubmitted to ApJ taking into account referee's
comment
The Sloan Lens ACS Survey. VIII. The relation between environment and internal structure of early-type galaxies
We study the relation between the internal structure of early-type galaxies
and their environment using 70 strong gravitational lenses from the Sloan ACS
Lens Survey. The Sloan database is used to determine two measures of
overdensity of galaxies around each lens: the projected number density of
galaxies inside the tenth nearest neighbor (\Sigma_{10}) and within a cone of
radius one h^{-1} Mpc (D_1). Our main results are: 1) The average overdensity
is somewhat larger than unity, consistent with lenses preferring overdense
environments as expected for massive early-type galaxies (12/70 lenses are in
known groups/clusters). 2) The distribution of overdensities is
indistinguishable from that of "twin" non-lens galaxies selected from SDSS to
have the same redshift and stellar velocity dispersion \sigma_*. Thus, within
our errors, lens galaxies are an unbiased population, and the SLACS results can
be generalized to the overall population of early-type galaxies. 3) Typical
contributions from external mass distribution are no more than a few per cent,
reaching 10-20% (~0.05-0.10 external convergence) only in the most extreme
overdensities. 4) No significant correlation between overdensity and slope of
the mass density profile of the lens is found. 5) Satellite galaxies (those
with a more luminous companion) have marginally steeper mass density profiles
than central galaxies (those without). This result suggests that tidal
stripping may affect the mass structure of early-type galaxies down to kpc
scales probed by strong lensing, when they fall into larger structures
[ABRIDGED].Comment: ApJ, in press; minor changes with respect to v
Християнські традиції паломництва в сучасній Білорусії (за матеріалами польових досліджень)
Іn the article are examined modern Christian traditions of pilgrimage in Byelorussia. There is given a characteristic of the features of the traditions of worship to the sainted places in the contemporary culture of Byelorussian ethnos, structure and functions of pilgrimage are investigated. The influence of pilgrim traditions on the ethnic processes is noted (consciousness of Belorussians). The author used the materials of the field ethnolographical expeditions as the main saurce of the investigation.У артыкуле разглядаюцца сучасныя хрысціянскія традыцыі паломніцтва ў Беларусі. Пад-час аналізу праблемы аўтарам выкарыстаны ў якасці асноўнай крыніцы матэрыялы палявых этнаграфічных экспедыцый. Даецца характарыстыка асаблівасцей традыцый пакланення святым месцам у сучаснай культуры беларускага этнасу, даследуюцца структура і функцыі паломніцтва. Адзначаны ўплыў паломніцкіх традыцый на этнічныя працэсы (самасвядомасць беларусаў)
The Sloan Lens ACS Survey. IX. Colors, Lensing and Stellar Masses of Early-type Galaxies
We present the current photometric dataset for the Sloan Lens ACS (SLACS)
Survey, including HST photometry from ACS, WFPC2, and NICMOS. These data have
enabled the confirmation of an additional 15 grade `A' (certain) lens systems,
bringing the number of SLACS grade `A' lenses to 85; including 13 grade `B'
(likely) systems, SLACS has identified nearly 100 lenses and lens candidates.
Approximately 80% of the grade `A' systems have elliptical morphologies while
~10% show spiral structure; the remaining lenses have lenticular morphologies.
Spectroscopic redshifts for the lens and source are available for every system,
making SLACS the largest homogeneous dataset of galaxy-scale lenses to date. We
have developed a novel Bayesian stellar population analysis code to determine
robust stellar masses with accurate error estimates. We apply this code to
deep, high-resolution HST imaging and determine stellar masses with typical
statistical errors of 0.1 dex; we find that these stellar masses are unbiased
compared to estimates obtained using SDSS photometry, provided that informative
priors are used. The stellar masses range from 10^10.5 to 10^11.8 M and
the typical stellar mass fraction within the Einstein radius is 0.4, assuming a
Chabrier IMF. The ensemble properties of the SLACS lens galaxies, e.g. stellar
masses and projected ellipticities, appear to be indistinguishable from other
SDSS galaxies with similar stellar velocity dispersions. This further supports
that SLACS lenses are representative of the overall population of massive
early-type galaxies with M* >~ 10^11 M, and are therefore an ideal
dataset to investigate the kpc-scale distribution of luminous and dark matter
in galaxies out to z ~ 0.5.Comment: 20 pages, 18 figures, 5 tables, published in Ap
The internal structure and formation of early-type galaxies: the gravitational--lens system MG2016+112 at z=1.004
[Abridged] We combine our measurements of the velocity dispersion and the
surface brightness profile of the lens galaxy D in the system MG2016+112
(z=1.004) with constraints from gravitational lensing to study its internal
mass distribution. We find that: (i) dark matter accounts for >50% of the total
mass within the Einstein radius (99% CL), excluding at the 8-sigma level that
mass follows light inside the Einstein radius with a constant mass-to-light
ratio (M/L). (ii) the total mass distribution inside the Einstein radius is
well-described by a density profile ~r^-gamma' with an effective slope
gamma'=2.0+-0.1+-0.1, including random and systematic uncertainties. (iii) The
offset of galaxy D from the local Fundamental Plane independently constrains
the stellar M/L, and matches the range derived from our models, leading to a
more stringent lower limit of >60% on the fraction of dark matter within the
Einstein radius (99%CL).
Under the assumption of adiabatic contraction, the inner slope of the dark
matter halo before the baryons collapsed is gamma_i<1.4 (68 CL), marginally
consistent with the highest-resolution cold dark matter simulations that
indicate gamma_i~1.5. This might indicate that either adiabatic contraction is
a poor description of E/S0 formation or that additional processes play a role
as well. Indeed, the apparently isothermal density distribution inside the
Einstein radius, is not a natural outcome of adiabatic contraction models,
where it appears to be a mere coincidence. By contrast, we argue that
isothermality might be the result of a stronger coupling between luminous and
dark-matter, possibly the result of (incomplete) violent relaxation processes.
Hence, we conclude that galaxy D appears already relaxed 8 Gyr ago.Comment: 8 pages, 4 figures, ApJ, in press, minor change
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